Cross-polarized normal mode patterns at a dielectric interface

Abstract

Basic features of narrow optical beam interactions with a dielectric interface are analysed. As it was recently shown, two types of paraxial beams – elegant Hermite-Gaussians of linear polarization and elegant Laguerre-Gaussians of circular polarization – can be treated as vector normal modes of the interface [1]. In this contribution the problem of normal modes is discussed with special attention paid for the case of beam oblique incidence. Excitation of higher-order modes by cross-polarization coupling is described and it is shown that this process critically depends on a propagation direction of the incident beam. Besides the expected changes of mode indices induced by generalised transmission and reflection matrices, the new phenomenon of optical vortex spectral splitting at the interface is revealed and off-axis spectral placements of the splitted vortices are determined. Results of numerical simulations given here for beam reflection entirely confirm theoretical predictions even for beams beyond the range of paraxial approximation.